Modern 6 speed automatic transmissions, how strong are they?

We are one of the only manufacturers of Hi Stall converters for the modern 6 speed automatics and we see a lot of interesting things and hear a lot of interesting stories about what you can and can’t do with them, so I thought this would be an interesting topic to discuss.

Firstly the GM (6L80E) and Ford (ZF6HP) transmissions are very similar, it appears that in usual style for the two marquees, Ford has opted to by the transmissions outright from ZF while GM has chosen to only buy the design and manufacture their own. In reality they are essentially the same transmission wrapped in different cases. The converters are totally different with GM sticking to its proven design philosophy’s in the torque converter and Ford choosing to use the ZF unit which is like most German units in that it is difficult to work on, hard to get parts for and expensive to fix.

Now most people don’t appreciate what is happening inside the transmission as you are driving down the road and this is where these modern 6 speed transmissions are totally different to any of their predecessors. These transmissions are a “Clutch on Clutch” type transmission, this means that for every gear change, one clutch needs to release as one clutch engages. This principal is employed on several sequential manual transmissions such as the latest F1 cars, the new R35 GTR and the new Lancer EVO 10.

The theory seems great but making it work correctly isn’t that easy hydraulically so the engineers employed electronics. Each shift is controlled by a solenoid that is controlled by the central ECU, sounds great but it’s not. You see manufacturers are really good at cost cutting and engineers are really good at making assumptions so what is missing from these systems that would make them nearly infallible is some sort of fold back so that the computer knows that the transmission has done what it has been commanded to do. The way these transmissions work is that the ECU assumes that the transmission has done what it has been commanded to do. This assumption poses a problem.

If both clutches are on at the same time then there will be a shift “Overlap” or “Bind” this is the most common cause of failure in these transmissions, if the clutches are both off at the same time there will be a shift “Flare”, once again a common cause of failure. All of these events are controlled by the ECU and when you have your ECU re-mapped or “Tuned” these parameters are quite often changed and the shift quality is often changed. In modified cars that have been tuned, most of the failures are caused by a bad tune, but a lot of failures are caused by factory faults that are built into the transmission, for example 3rd gear clutch clearance is usually not correct on either of these units from new and the factory parameters for the 2-3 shift is not correct so premature wear in 3rd gear clutch pack is a factory fault.

I have driven cars that have had transmission tunes done by various workshops across Australia and there is a vast difference between the ones that are tuned correctly and the ones that aren’t. When the vehicles are tuned correctly, at light throttle, it almost feels like a seamless shift, when they are not and even in some factory un-tuned vehicles the shift can be quite harsh and feel as though the vehicle is slowing down before it starts speeding up again. This is why fold back systems would have been a smarter choice by the manufacturers so that the ECU could constantly monitor pressures in each clutch and keeps tabs on if the transmission was doing what it is being told to do.

None the less one thing that you can guarantee is that at some stage or another you will need to have your transmission rebuilt and it is very easy to get ripped off, I have heard of people spending over $10,000 to cure a $100 problem!

Firstly, beware of “Buzz” words; we hear them all the time, “Cryogenically treated”, “Hardened”, “Aftermarket”, “Special”. Chances are that if you can’t find the manufacturer for the part that you’re about to pay $1000’s for on the internet then it probably doesn’t exist and the only thing that is special is the bus you should be riding on for believing the crap that you have been fed. These transmission are expensive to rebuild if you are doing them properly and if you have to replace a lot of parts but if your car just lost drive, chances are that only one part has broken.

There are two categories of parts within any automatic transmission, “Hard” parts and “Soft” parts, Hard parts are the shafts, drums, etc while soft parts include the clutches, the steels, the seals. Not much goes wrong with the hard parts unless there has been a catastrophic failure or the transmission has got a million miles on it and has just pain worn out. Most of the common ailments in the modern 6 speed transmission stem from the factory 3rd gear clutch pack clearance being too loose, this can be corrected in the tune and actually be fixed that well that the transmission will last longer than it will in a stock car, or fail in 5 minutes if the vehicle is tuned by an idiot.

So the bottom line is be careful, make sure you’re not being conned and use some logic when you’re making a decision. If you call ten shops and they all tell you that the transmission you’re using isn’t strong enough for the power you’re making, but the 11th shop says that they have a “Special” part that makes it stronger, the 11th shop is probably lying to you. If your trans was fine and failed immediately after the tune, then the tuner may have caused the problem (not always, I mean if the car already has 100,000k’s on it then it was bound to happen anyway!). If the shop they send you too to get the work done on the trans promises the world to you, chances are you’re about to be getting the trans built more than once. Use your common sense, if a deal is too good to be true, it usually is!

Lastly, be realistic, most OEM (Original Equipment Manufacturer) transmissions will handle about 30% more power than factory, so if your car makes 300Kw factory and now it makes 390Kw, the factory trans will probably take the power if it has been tuned correctly and if you don’t abuse it, but if your car is now making 500Kw then the trans will probably break and keep on breaking; the smart guys will change to a transmissions that is designed to handle that kind of power from day one. Powerglide and Turbo 400 transmissions are the 2 most common transmissions when your engine exceeds 500Kw not much else will handle the power, the components used in these transmissions (when built by professional race transmission shops) have been developed over the last 40 years to take the extreme punishment of modern drag racing and can be built to handle over 1000Kw.

See you on the street.